Primary control for burners



1951 J. J. ROTHWELL EIAL 2,578,947

PRIMARY CONTROL FOR BURNERS 2 SHEETS-SHEET 2 Filed Oct. 17, 1945 i Z 7Aif E N Z Patented Dec. 18, 1951 PRIMARY CONTROL FOR BURNERS John J.Rothwell, Elkhart, and Leland B. Wagner, Goshen, Ind., assignors to PennElectric Switch 00., Goshcn, Ind., a corporation of Iowa ApplicationOctober 17, 1945, Serial No. 622,888

3 Claims.

This invention relates for burners to take the switch having a "slip" toa control structure place of the. usual stack or friction connection.

One object of our invention is to provide a combined combustion switchand safety switch which may be connected in a burner control circuit soas to deenergize the circuit as a result of combustion failureinitially, combustion failure after establishment, or failure of asafety heater such as a burned-out condition thereof.

Another object is to provide a primary" control for a burner which issimple in construction and inexpensive to manufacture, and which hasimproved constructional and operational characteristics when comparedwith the burner control system shown in our Patent No. 2,367,059, issuedJanuary 9, 1945.

A further object is to provide a controller which is arranged to responddirectly to the heat of combustion by exposing a bimetal element of theprimary control to heat from a combustion chamber, it being unnecessaryto locate the control inside a stack or inside the combustion chamber,but merely externally of the combustion chamber with an opening throughthe wall thereof to expose the bimetal element to the heat therein, thebimetal element responding to the combustion chamber temperature andanother bimetal element responding to a safety heater, both beingenclosed within a housing which assures substantially constant operatingcharacteristics for the primary control so that it operates properlyunder all conditions.

Still a further object is to provide a primary control of this generalcharacter which may be either of the recycling type or of the lock-outtype, requiring reset before recycling after a shut-down caused bycombustion failure.

An additional object is to provide a combustion switch which utilizes apair of bimetal elements or difierent parts of one bimetal element forresponse to two difierent conditions, 1) the combustion heat, and (2)the heat from an electrically energized heater, the parts being soassociated in a control circuit that the desired opening of the circuitis had upon combustion failure either prior to or subsequent tocombustion establishment.

With these and other objects in view, our invention consists in theconstruction, arrangement and combination of the various parts of ourprimary control whereby the objects contemplated are attained, ashereinafter more fully set forth, pointed out in the claims andillustrated in the accompanying drawings, wherein:

Fig. 1 is a plan view of a primary control embodying our presentinvention and showing an electrical diagram of a burner circuit inconnection therewith;

Fig. 2 is a vertical sectional view on the line 2 2 of Fig. 1;

Fig. 3 is a vertical sectional view on the line 33 of Fig. 2;

Fig. 4 is a diagrammatic view similar to a portion of Fig. 2 showing theparts in the position they assume upon combustion establishment;

Fig. 5 is a similar diagrammatic view showing the position of the partsupon combustion failure;

Fig. 6 is a plan view of a modified form of the invention;

Fig. 7 is a vertical the line 'l 1 of Fig. 6;

Fig. 8 is a vertical 88 of Fig. 7.

On the accompanying drawings we have used the reference numeral II) toindicate a furnace wall or the wall of a combustion chamber, which wallhas an opening 12 cut therein. Our primary control, indicated generallyat PC, includes a housing It having a flange l6 secured to a plate 48,as by rivets 20, with a heat insulating gasket 22 between the two. Theplate IS, in turn is secured as by screws 24 to the furnace wall I 0,with an opening 25 in the plate l8 registering with the opening I2 sothat radiated and conducted heat can pass through the openings [2 and 25into the interior of the housing l4. Surmounting the housing I 4 is asecond housing 26 adapted to contain switch mechanism, as will behereinafter described. A cover 21 is provided for the housing 26 andthis cover has been omitted from Fig. 1.

The switch housing 25 serves as a support for a bimetal element 13, ashield S and a heater H, all of which depend from the housing 26. Withinthe housing 26 a permanent magnet 28 is supported for snap-actingcooperation with an armature 30, which armature is secured, as by screws32, to a central section 34 of the bimetal element B.

The section 34 is shown formed in four strips. The bimetal element B hastwo other sections 36 formed in two strips. The entire bimetal elementis thus in the form of a W, having two connecting portions 38 atthebottom for the sections 34 with relation to the sections 36. A pairof bars 40 is then secured along the bottom of the bimetal element forreinforcing it. The upper ends of the sections 36 are anchored to abracket 42, as by screws 44.

sectional view thereof on and sectional view on the line The armature 30carries a movable contact 48 for coaction with a stationary contact 50mounted on a bracket 52. The bracket 52 is connected by a strap 54 witha screw 56 to which a bracket 58 is secured for supporting the heater Hand for connection to one end of the resistance wire in the heater. Theother end of the resistance wire is connected to a second bracket 60which, in turn, is connected to a screw 62 and a strap 64 extends fromthe screw 62 to a terminal 66. A second terminal 68 is provided on thebracket 42, which bracket supports the bimetal element B so that acircuit can be traced from the terminal 66 through the elements 64, 62,60, H, 58, 56, 54, 52, 50, 48, B, and 42 to 68. This places the contacts48 and 50 in series with the heater H, and the two are in a controlcircuit, as shown in Fig. l, which includes, in series, a roomthermostat RT, a secondary S of a step-down transformer T, and a relaycoil RC. The circuit also includes current supply wires and 12 for aburner motor BM, its ignition mechanism Ign and for the primary P of thetransformer T. The burner motor EM and the ignition mechanism Ign arecontrolled by a motor switch MS which is normally open and closes inresponse to the relay coil RC being energized.

In the combined combustion and safety switch shown in our patenthereinbefore' mentioned there was no casing for the bimetal elements,and it was found that they were sometimes erratic in action. This wasparticularly true due to the temperature ambient to the bimetal elementsvarying as by differences in the draft through the furnace, and passingair currents surrounding the furnace. It will be noted in the presentapplication that we have entirely enclosed the bimetal element B withinthe housing [4, with the exception of the opening 25.

This places both portions 34 and 36 of the bimetal element in the sameambient temperature, and that ambient temperature is isolated from thesurrounding atmosphere while, at the same time, both sections of thebimetal are subject to the furnace temperature through the opening 25.It is necessary, however, that the bimetal element section 34 respondmainly to heat from the heater H, whereas the element sections 36respond mainly to the heat of combustion. This is accomplished byleaving the sections 36 unobstructed for direct radiation of heat fromthe interior of the combustion chamber while shielding the elementsection 34, as by the shield S. This shield has a wall 14 facing theheat from the combustion chamber. The wall 14 has a pair of side wings16 to isolate the bimetal section 34 from direct rays of heat from thefurnace. However, both bimetal element sections 34 and 36 are subject tothe general temperature within the housing l4 so that regardless ofwhether that temperature is low, as when starting the furnace, or high,as after it has operated a considerable time period, both bimetalelements in so responding compensate/for the ambient temperature inwhich they are located, as will be hereinafter more fully described.

The type of control shown in Figs. 1, 2 and 3 has a snap-acting switchwhich returns to closed positions after a flame failure when the partscool down again. It is more desirable, however, to have the switch lockout so that whatever caused the flame failure can be remedied, and theswitch then reset.

In Figs. 6, '7 and 8 we show a modified form of the invention foraccomplishing this result. In

d place of an armature and magnet, snap action is secured by a togglemechanism consisting of a toggle lever l8 pivoted by means of knife edgepivots at 86 to a stationary vertical flange 82. A toggle spring 85connects a transverse portion 86 of the toggle lever 18 with a notchedportion 88 of the vertical flange 82, and the toggle lever is normallyin the position shown in Fig. 6 against a stop screw 30.

In place of the armature 36 an extension 92 from the bimetal section 34is adapted to contact the right-hand end of the toggle lever 56 and moveit upwardly in Fig. 6 for causing an adjusting screw 94 carried therebyto slide a pin 66 lengthwise through a perforation 98. The pin 96thereupon engages'a leaf spring 566 which has the movable contact 48mounted thereon and normally engagedwith the stationary contact 55.

The parts 34, 48 and 50 correspond to those in the first three figuresof the drawing, and other parts of this form of structure alsocorrespond to parts of the first three figures, and, accordingly, bearthe same reference numerals. The contact 50 is mounted on leaf spring12. The spring I02 and the spring I66 are connected in the circuit, asin series with the heater H, in a manner similar to that alreadydescribed.

When the toggle lever 18 is rocked counterclockwise from the positionshown in Fig. 6, due to combustion failure, it stays in that position,thus holding the contact 66 separated from the contact 50. The troublemust then be remedied and the device reset. Reset is accomplished bymeans of a slidable reset bar Hi4 having a pair of ears M6 to engage aflange 568 on the pin 36. The pin can thereby be pushed downwardly inFig. 6 to return the toggle lever 18 to its original position shown bysolid lines. At the same time. an ear H6 on the reset lever Hi6 engagesthe leaf spring I02 to hold the contact 50 away from the contact 48 toprevent the possibility of manually holding the contacts closed while adangerous condition of the furnace prevails. A spring W9 is provided forreturning the reset-lever 866 to its initial position.

PRACTICAL OPERATION Normal burner operation In the operation of ourinvention, when the parts are in the cold position of Figs. 1 and 2, thecontact 48 is held under pressure against the contact 50 due to therelative settings of the mounting bracket for the bimetal element B andthe desired tension in the bimetal for contact pressure. The secondarycircuit of the transformer is thereby ready for operation whenever theroom thermostat RT closes. Upon closure of the room thermostat a circuitmay be traced from the top of the secondary coil S through the roomthermostat, the heater H and the relay coil BC in series, therebyclosing the motor switch MS so that the burner motor BM and its ignitionmechanism will operate.

Energization of the heater H causes the bimetal element portion 34 tobecome warped, as shown by solid lines in Fig. 4, the position of theheater in relation to the bimetal, and the heat transfer relation of theheater being so selected that the warping of the bimetal element is comparatively slow. The heat flow is indicated by arrows a.

In the meantime, burner operation has been successfully established andthe radiant heat flow from the combustion chamber, indicated by thearrows 1), causes heating of the bimetal element sections 36 so thatthey too warp to approximately the same curvature as the section 34whereupon the composite element B assumes the dotted position of Figure4. At the same time both bimetal element sections are heated by heatfrom the furnace, both sections being within the housing l4 are therebysubject to the general temperature within this housing as it rises inproportion to a rise of furnace temperature which merely increases thedotted curvature in Figure 4 all the way up to the point where thetemperature becomes stabilized without changing the position of theupper end of the section 34. We have found that location of the twobimetal element sections in the same ambient temperature, and thattemperature stabilized as by complete enclosure within a housing, isnecessary for proper operation at all times, and have further found thatthe housing surrounding the bimetal element sections should becompletely opened for the reception of direct heat rays from theinterior of the furnace without any intervening wall of glass or thelike which might become smoked and cut down heat transmission. As to thebimetal element sections 36, they operate best when blackened, as theythen have maximum heat absorption qualities and operate mostefiiciently.

In addition to the general subjection to ambient temperature within thehousng I4, the sections 36 of the bimetal are definitely responsive toradiant heat from the combustion chamber. The 'combustion heat transferto the sections 36, as indicated by the arrow b, causes these sectionslikewise to warp so that the upper end or armature 30 of the bimetalremains in positionfor keeping the contacts 48 and 50 closed. The magnet28, acting on the armature 30. also aids in retaining a closed circuitand increases the initial contact pressure in addition to the tension inthe bimetal.

Thus, during normal burner operation the contacts 48 and 50, which maybe termed safety contacts are retained closed, and, subsequently, whenthe room thermostat opens the relay coil is deenergized to thereby openthe motor switch and stop the burner. The bimetal B then cools down,returning to its original position, as in Fig. 2. When the burner onperiods are extended both bimetals will warp to a further curvature, asshown by dotted lines in Fig. 4, thus still maintaining the contactsclosed, and since both bimetal sections are subject to the furnacetemperature, both will be warped substantially equal. Their relativesizes and the size of the shield S may be varied to secure the desiredresults.

Failure of combustion to be established Referring to Fig. 5, ifcombustion does not occur in the normal manner the bimetal elementsections 36 will remain in their cold positions while the bimetalelement section 34 will move to its hot position, due to energization ofthe heater H. This will take preferably about a minute or so, althoughthe time does not have to be as long as it takes the usual safety switchin a stack switch installation to drop out. The room thermostat circuitis now opened across the safety switch contacts 48 and 50 so that therelay coil is deenergized, thus opening the motor switch.

After a time period, predetermined by the length of time it takes theheater H and the bimetal element section 34 to cool down, the con- 6trol circuit will be reestablished, thus providing a purging period andthereby permitting an at tempt at another start of the burner.

In the form of device shown in Figs. 6 and 7, after the contacts 48 and50 are separated they will remain so, as return of the element 92, dueto cooling down of the bimetal element section 34, merely causes theelement 92 to walk away from the toggle lever 18. The toggle springbeing over-center in the opposite position from that shown in Fig. 6will cause the contacts to remain open until such time as they are resetby pushing in on the lever I04 after the trouble has been remedied.

Combustion failure after establishment Referring to Figs. 4 and 5,wherein Fig. 4 shows combustion having been established, if there is asubsequent failure of combustion the bimetal element sections 36 willstraighten out again as to the position of Fig. 5, thereby opening thesafety switch contacts 48 and 50 for shutting down the burner for apurging period, or with the construction of Figs. 6 and 7 for alock-out. The flame failure, of course, permits the combustion chamberto cool down and the bimetal element sections 36 thus become cooledwhile the section 34 remains heated due to continued energization of theheater H. Thus the contacts 48 and 50 take the place of both the safetyswitch contacts and the combustion switch contacts in the usual type ofstack switch hav ing a thermal responsive element in the stack and anindividual safety switch with its separate contacts, the safety switchincluding a heater which is not connected with the combustion switchexcept in the electrical circuit. In our device, on the other hand, thebimetal element is so arranged that it responds both to a heater andcombustion temperature in such manner that a single set of contactsserve as a control in response to combustion and a safety switch inresponse to current through a heater. Our primary control hereindisclosed is therefore, in effect, a combined combustion switch andsafety switch in which the contacts 48 and 50 are separated as a resultof a cold combustion chamber and a hot heater. Whenever these two eventsoccur at the same time the burner is shut down. whereas during normalcycling of the burner the contacts remain engaged and are neverseparated. Separation occurs only when there is either an initialcombustion failure or a combustion failure subsequent to establishmentthereof. Our arrangement is such that we have the primary controlresponsive to combustion chamber temperatures from a point exterior ofthe combustion chamber where the temperatures range only from 70 to 700F. Our control entirely eliminates a slip connection and is so designedas to combine a warp type of safety switch with a combustion responsiveelement so as to use a single set of contacts, which contacts aremaintained in proper relation to each other, regardless of temperatureambient to the bimetal element sections. The bimetal may be a singlepiece made in sections, as disclosed, or made of two or more piecesconnected together to secure the same results and may warp toward theheater and the combustion chamber instead of away from them, asdisclosed in Figs. 4 and 5.

We have found that rather wide variations in combustion chambertemperatures and heater temperatures do not materially affect operationof the primary control, providing the bimetal aerate? long as thatambient is stabilized as by being open to the interior of the combustionchamber. The housing for the bimetal sections eliminates the possibilityof stray air currents and changes element in direct communication withthe in-v terior of the furnace without any intervening 'windowsoi glassor the like, all possibility of failure of operation due to reduction inheat flow from thecombustion chamber to the bimetal element iseliminated, and regardless of what temperature the furnace attains, thebimetal element is always self-compensating, as both sections 39 and 36,being subjected to the furnace temperature, warp substantially equallyin spite of the element '34 being shielded by the shield S from thedirect rays of heat from the combustion chamber. It is a simple matterto connect the controller into the circuit for controlling -it in amanner similar to that had from a regulation stack switch. 7

Some changes may be made in the construction andarrangement of the partsof our burner control system without departing from the real spirit andpurpose of our invention, and it is our intention to cover by our claimsany modified forms of structure or use of mechanical equivalents whichmay be reasonably included within their scope.

We claim as our invention:

1. A primary control for burners comprising a bimetal element having apair of side-by-side sections connected together at one end, the otherend of one section being anchored and the other end of the other sectionconstituting an actuating element, a combustion switch having switchcontacts which are openable by said actuating element, an electricheater, one of said bimetal element sections being responsive to heatfrom said electric heater, and a common housing for both of said bimetalelement sections whereby both sections are subject to the same ambienttemperature therein, said housing having an opening through which heatmay be radiated to actuate the other of said bimetal element sections,and a shield in said housing between said opening and said first bimetalelement section.

2. In a burner control, a combustion switch, a heating element, saidcombustion switch comprising a pair of thermal elements arrangedside-byside in substantially the same plane, connected sections are bothin the same ambient, and as together at one end and the other end ofeach being anchored and free respectively, said combustion switch havingcontacts controlled by said free end, a housing for both of said bimetalelements and having an opening, a shield for one oisaid bimetal elementsto shield it from direct rays through said opening, said heating elementbeing located adjacent said one of said bimetal elements to heat thesame predominantly with respect to heat through said opening, saidelements when responding to a normal burner operating condition movingin the same direction with said contacts remaining closed, heating ofsaid heating element and cooling ora cold condition through said openingmoving said bimetal elements unequally and thereby effecting separationof said contacts.

3. In a primary control for burners, a combustion switch comprising apair of side-by-side thermal elements, contacts controlled thereby, ahousing having an opening, both of said thermal elements being housedtherein for response to temperature therein, one of said thermalelements being located to have an unobstructed and direct path throughthe air from said opening to the element, obstructing means between theother element and said opening, and a heating element located adjacentsaid other element to heat the same when energized with an amount ofheat which is in addition to that indirectly absorbed by thethermal-element through said opening.

JOm J. ROTHWELL. 1 i B. WAGNER.

REFERENCES (CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,576,056 Liefke Mar. 9, 19262,041,559 Marks May 19, 1936 2,095,846 Westendorp Oct. 12, 19372,098,383 Furlong Nov. 9, 1937 2,159,392 McCabe May 23, 1939 2,162,098McCabe June 13, 1939 2,227,901 Hageman Jan. '7, 1941 2,267,463 Hood eta1. Dec. 23, 1941 2,281,319 Newell Apr. 28, 1942 2,284,383 Elmer May 26,1942 2,302,399 Stimson Nov. 17, 1942 2,367,059 Rothwell et al Jan. 9,1945

